cellAttributes fix for #107, individual layout template fix for #106

[webdevilopers]

Sorry for putting both fixes in one PR. I'm new to github usage for multiple PRs.
I guess it's best practice start a separate branches named patch-X, right?

Fix 1 adds the following valid cellAttributes to the column renderer:

• sorttype
• summaryType
• summaryTpl

Though valid strings are defined their validation is not implemented yet.

These callattr quickly allow the user to use jqgrid's summary feature on the footerrow.
See Grouping -> Summary Footers here: http://trirand.com/blog/jqgrid/jqgrid.html

Still groupingView parameters have to be added to the jqgrid templatee.g.:

javascript
grouping:true, groupingView : { groupField : ['name'], groupSummary : [true], groupColumnShow : [true], groupText : ['{0}'], groupCollapse : false, groupOrder: ['asc'] },

A quick fix to issue https://github.com/ThaDafinser/ZfcDatagrid/issues/107 .

Fix 2 allows the user to set an individual layout directely on the `DataGrid`:

``` php
$grid = $this->getServiceLocator()->get('ZfcDatagrid\Datagrid');
$grid->setTemplate('application/index/list');

[webdevilopers]

@ThaDafinser If you can confirm that the following issue is the official way to set an individual layout
#106
then you can close this PR and I will create a new separate patch for the cellAttributes fix.

[ThaDafinser]

You can set custom templates with this line

$grid->getRenderer()->setTemplate('your-template')

It must be set for each renderer, since each renderer has its own template

@webdevilopers integrating custom grouping for only one renderer is not good, since we need at least export support for it